Reaction to “Signal detection theory and the psychophysics of pain” by Lloyd & Appel (1976)

Reaction to Lloyd & Appel (1976) by Richard Thripp
EXP 6506 Section 0002: Fall 2015 – UCF, Dr. Joseph Schmidt
October 7, 2015 [Week 7]

Lloyd and Appel (1976) review many articles involving signal detection theory and pain research, reaching the conclusion that greater methodological consistency is needed (p 79). This seems a valid point—3 of 9 of the studies from Table 2 (p. 89) did not even report (and may not have used) a zero pain stimulus, so how can they make inferences about pain detection without even knowing what their subjects report at the baseline? The authors rightly criticize the existing literature for other issues such as too few repetitions and lack of consistent standards for SDT measures (p. 88). Further, d′ itself (the sensitivity measure) tends to be higher with a binary measure than a rating system with more categories (p. 90)—to the point that using both types of measures simultaneously has been advocated. Few if any of the available articles considered this.

Unfortunately, the authors fail to draw sufficient connections between the articles or critically analyze them as a whole, in my opinion. While several connections and comparisons are made, there is no real discussion section to synthesize the research, and the “summary and conclusions” section is less than a single page. While this may be partly forgiven due to a scarcity of SDT research as of 1976, the authors discussed at least 13 articles, which may be enough to attempt such a synthesis. We do have a “Summary of Criticisms” table (p. 89) that helps us identify possible flaws in nine of the articles. Unfortunately, this table is half-baked—all cells are binary “Yes” or “No” data, without any indications of magnitude in columns such as “change in sensitivity” and “change in response bias.” Though yes/no might be a welcome relief from the overwhelming quantity of numbers in recent cognitive psychology literature, the authors could have, at minimum, used superscripts and footnotes to indicate particularly large changes or egregious methodological problems. Further, though an accurate criticism of much of the research, what constitutes “sufficient stimulus presentations” is not specified in the table. Finally, the authors included a table only for the nine modification studies they reviewed (pp. 84–91), neglecting to include a table for the four normative and comparative studies (pp. 91–92).

Lloyd and Appel have produced a strong primer on signal detection theory, complete with copious graphs and figures (pp. 80–84). It would be nice to see some of this explanatory power applied to the literature review, which is devoid of graphs and figures. For instance, they could have provided bar graphs comparing sensitivity and response bias for the different studies by Clark and associates involving diazepam, suggestion, and acupuncture (pp. 85–87). While the authors have explained that comparisons are difficult due to different standards between the studies (p. 88), it seems that studies with the same principal investigator (Clark) should be easier to compare. Nevertheless, the authors have vocalized solid criticisms, and I found the section discussing response biases and placebo effects to be particularly cogent (p. 84).


Lloyd, M. A., & Appel, J. B. (1976). Signal detection theory and the psychophysics of pain: An introduction and review. Psychosomatic Medicine, 38(2), 79–94.

Leave a Reply

Your email address will not be published. Required fields are marked *